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    <title>cdfpoi</title>
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    <center>Scilab Function</center>
    <div align="right">Last update : Dec 1997</div>
    <p>
      <b>cdfpoi</b> -  cumulative distribution function poisson distribution</p>
    <h3>
      <font color="blue">Calling Sequence</font>
    </h3>
    <dl>
      <dd>
        <tt>[P,Q]=cdfpoi("PQ",S,Xlam)  </tt>
      </dd>
      <dd>
        <tt>[S]=cdfpoi("S",Xlam,P,Q)  </tt>
      </dd>
      <dd>
        <tt>[Xlam]=cdfpoi("Xlam",P,Q,S);  </tt>
      </dd>
    </dl>
    <h3>
      <font color="blue">Parameters</font>
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    <ul>
      <li>
        <tt>
          <b>P,Q,S,Xlam</b>
        </tt>: four real vectors of the same size.</li>
      <li>
        <tt>
          <b>P,Q (Q=1-P)  </b>
        </tt>:  The cumulation from 0 to S of the poisson density. Input range: [0,1].</li>
      <li>
        <tt>
          <b>S</b>
        </tt>:Upper limit of cumulation of the Poisson. Input range: [0, +infinity). Search range: [0,1E300]</li>
      <li>
        <tt>
          <b>Xlam</b>
        </tt>:  Mean of the Poisson distribution. Input range: [0, +infinity). Search range: [0,1E300]</li>
    </ul>
    <h3>
      <font color="blue">Description</font>
    </h3>
    <p>
    Calculates any one parameter of the Poisson
    distribution given values for the others.</p>
    <p>
    Formula   26.4.21  of   Abramowitz  and   Stegun,   Handbook  of
    Mathematical Functions (1966) is used  to reduce the computation
    of  the cumulative distribution function to that  of computing a
    chi-square, hence an incomplete gamma function.</p>
    <p>
    Cumulative  distribution function  (P) is  calculated  directly.
    Computation of other parameters involve a seach for a value that
    produces  the desired value of  P.   The  search relies  on  the
    monotinicity of P with the other parameter.</p>
    <p>
    From DCDFLIB: Library of Fortran Routines for Cumulative Distribution
    Functions, Inverses, and Other Parameters (February, 1994)
    Barry W. Brown, James Lovato and Kathy Russell. The University of
    Texas.</p>
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